Melting And Boiling Point Laboratory Guide - Alquimialab
Melting and boiling point Laboratory Guide
BÜCHI Labortechnik AG Version A
Contents 1 2 Introduction 3 1.1 What is a melting point? 3 1.2 Why measuring melting points? 3 1.3 Who measures melting points? 4 1.4 The boiling point 5 Theoretical basis for the measurement of boiling points and melting points 6 2.1 Physical states 6 2.2 Phase transitions 7 2.2.1 Phase diagrams for 1-material systems (state diagrams) 8 2.3 What happens during melting? 9 2.4 The boiling point – what happens during evaporation? 10 2.5 The range between the boiling and the melting point 12 2.6 Melting point depression and the mixed melting point 13 2.6.1 Melting point depression 13 2.6.2 Mixed melting point 13 2.6.3 The eutectic point 14 3 Principles and methods of melting point determination 15 3.1Methods of melting point determination 15 3.1.1 Determining the melting point in the capillary tube 16 3.1.2 Immediate melting point 16 3.2 Principles of melting point determination 18 3.2.1 Melting point determination according to the pharmacopoeia 19 3.2.2 Thermodynamic determination of melting points 20 3.3 Melting point determination yesterday and today – an overview 21 3.3.1 Instruments for melting point determination over the course of years 21 3.3.2 From silicone oil to the metal block 21 4 Melting point determination using the BUCHI M-565 23 4.1 Operating principle of the BUCHI M-565 instrument 24 4.1.1 Automatic determination of melting point 24 4.1.2 Metal heating block 25 4.2 Structure of the BUCHI Melting Point M-565 25 4.3 Melting point determination procedure with the BUCHI M-565 26 4.3.1 Sample preparation 26 4.3.2 M-565 device settings 27 4.3.3 Measurement according to US Pharmacopeia 29 4.3.4 Calibration and verification of the Melting Point M-565 instrument 32 4.4 Flow charts for a melting point determination with the BUCHI M-565 33 4.4.1 Substance with a known melting point or range 34 4.4.2 Substance with an unknown melting point or range 35 4.5 Boiling point determination with the BUCHI Melting Point M-565 36 4.6 Data quality – accurate control 37 4.7 Technical terminology 39 4.8 List of Melting Point M-560/565 instruments, accessories and spare parts 41 4.8.1 Instruments 41 4.8.2 Accessories 41 4.8.3 Spare parts 42
4 Melting Point Laboratory guide 1 Introduction 1.1 What is a melting point? There are several material constants that can be used to describe a material, for example, its specific gravity, light refraction, adsorption capacity, or chromatographic behavior. The melting point is also one of these constants. Along with the boiling point and the solidification point, it is one of the important thermal characteristics that describe a material. The melting points of many pure materials can be measured with great accuracy. Crystalline materials consist of extremely fine particles that form a certain regular 3-dimensional structure. These 3-dimensional arrangements are referred to as lattice structures or (crystalline) lattices. The particles within the lattice are held together by lattice forces. Whenever this solid structure, the lattice, is heated, the particles in it begin to move more strongly, until finally the forces of attraction between them are no longer strong enough to maintain the crystalline structure. The lattice is destroyed and the solid material melts. At the melting point a material shifts from its ordered, solid state to an unordered, liquid state. The stronger the forces of attraction between the particles within the lattice, the greater the amount of energy that must be used to overcome them. The melting temperature of a crystalline solid is thus an indicator for the stability of its lattice. The higher the temperature, the more strongly the lattice structure in question holds together. 1.2 Why measure melting points? There are various methods of chemical and physical analysis used to differentiate, identify, and classify materials. Measurement of the melting point is, among other things, one of these standard laboratory procedures. It is an experimental and easily performed method of physical analysis used to find out the identity, the purity, and the thermal stability of a material. Identification Pure materials have exactly defined melting points which can be obtained from reference tables. Thus, the identity of a material can be determined by measuring its melting point: One needs only to compare the melting point of the substance as determined in the test with the values in the technical literature. Of course, determination of the melting point alone is not yet enough for the clear identification of a substance. There may be several substances with the same melting point. In such cases, the shift in the mixed melting point (refer to Sect. 2.6.2) can provide an indication about the definitive identification of the material. Purity Even slight impurities in a material cause a lowering of its melting point or at least a widening of its melting range (the material melts within a range of temperatures and not at a precisely definable melting point). BÜCHI Labortechnik AG Version A
Melting Point Laboratory guide 5 This phenomenon is used to obtain indications about the purity of a material: The smaller the difference between the measured melting point of the substance and the melting point shown in the tables, the narrower its melting range and thus the purer the material. Thermal stability Many materials change at high temperatures, e.g., decomposition or discoloration. Measurement of the melting point is one method that can be used to determine how much the material can be heated without causing chemical changes. This value is useful as an indicator for the thermal stability of a substance and can be used to suggest a possible temperature for drying. 1.3 Who measures melting points? Various groups of users use melting point determination in their daily work with chemical substances. Their priorities and their specific requirements for how the melting point is to be determined may differ. The needs of users are different, especially with regard to accuracy of measurement and the ability to observe how the substance behaves during the measurement process. Synthesizing laboratories A traditional research laboratory continually produces new types of chemical compounds. In order to find out how these new compounds behave, the research scientists observe the melting process closely. Often, these researchers are dealing with different substances: They receive about 1 to 4 samples each week for investigation. Thus, having a high degree of automation for the measurement of melting points is only of secondary importance for them. Far more important is their ability to observe the sample comfortably during the melting process. Analytical laboratories Analytical laboratories perform the tests done on the receipt of goods (raw products) and when examining the end products of a production process. Their main interest here is checking the purity of the products. Their measurements must be as precise as possible. These laboratories analyze from 10 to 50 samples each week, whereby determination of the melting point is part of their daily routine. Because they are examining the same materials over and over again, a high degree of automation is an important advantage for them. Normally, these researchers do not need to observe the samples while measuring the melting point. Frequently, the substances they have to investigate are discolored or decomposing so that no automated determination of the melting point is possible. In this case, visual melting point determination may be considered. Pharmacies A mistaken identification of medication in pharmacies can become a danger for the health of patients. It thus becomes extremely important to verify the identity of the medications and agents. Measurements of melting points done in pharmacies therefore require both maximum accuracy and an opportunity to observe the melting process when necessary. BÜCHI Labortechnik AG Version A
6 Melting Point Laboratory guide 1.4 The boiling point All elements and many inorganic and organic compounds have characteristic boiling points, which can be obtained from reference tables. Mixed liquids do not have a precisely defined boiling point. Instead, they boil over a fairly wide range of temperatures within clearly defined boiling limits. Accordingly, observation of their boiling behavior is an easily measurable experimental criterion for determining their purity. Whenever the boiling temperature changes during the boiling process, the material you are investigating cannot be a single pure material. However, it must be noted that impurities basically have less effect on the boiling point than on the melting point. For that reason, the boiling point is less as informative criterion for the purity or for the description of materials as the melting point. BÜCHI Labortechnik AG Version A
Melting Point Laboratory guide 2 Theoretical basis for the measurement of boiling points and melting points 2.1 Physical states 7 The «physical state» of a material is the state in which the material exists under the given external conditions (pressure/temperature). A distinction is made here between «solids», «liquids», and «gases». Solids Liquids Gases Defined volume Defined volume No defined volume Defined shape No defined shape No defined shape Particles have a defined position Particle can shift positions with respect to one another Particles can move freely; there is no longer any reciprocal attraction present Table 1: Comparison of properties of the physical states «solid», «liquid», and «gaseous». The kinetic energy of the smallest particles, the compressibility of the material, and diffusion within the material increases as you go from left (solids) to right (gases). In general, a material may be present in any of these three physical states (Fig. 1). When the external conditions change, materials can undergo a physical state. This process is referred to as «phase transition». A change in physical state always entails taking up or giving off a considerable amount of energy. Figure 1: Changes in state: Transitions between the various physical states. BÜCHI Labortechnik AG Version A
8 Melting Point Laboratory guide Most materials are crystalline when solid, i.e., in that state, their smallest particles (atoms, molecules, or ions) form an orderly, 3-dimensional arrangement – a crystalline lattice. The stability of the lattice depends not only on how strong the forces between two components of the grid are between themselves, but also on how uniformly these forces act in all directions in space. In addition to crystalline solids, there exist also amorphous solids, whose particles are in a random arrangement in the solid state. Glass, resin, and many synthetic plastics are examples of amorphous materials. 2.2 Phase transitions The «phase» or physical state refers to material that is homogeneous in chemical composition and in a spatially constant physical condition. As already mentioned, materials may transform from one phase into another by means of phase transition. A phase transition always takes up or gives off energy (the heat of melting or evaporation, and/or the heat of condensation or solidification, cf. Sect. 2.3) and always occurs at the same pressure for any given temperature. The density of materials also changes during phase transitions. During the actual transition, the two physical states (phases) of the material always exist side-by-side, and the temperature remains constant until the change in phase has been completed. A temperature/energy diagram shows these relationships. Figure 2: Temperature/energy diagram. BÜCHI Labortechnik AG Version A
Melting Point Laboratory guide 9 2.2.1 Phase diagrams for 1-material systems (state diagrams) The phase transition point is where the different phases, or physical states, of a material, interchange depending on external driving forces. The vapor pressure of a material indicates the number of molecules per unit of volume that are present in the gas zone in a state of equilibrium. It therefore indicates the tendency of the particles to pass over from a liquid or a solid phase into the gas phase, and is an indicator for the strength of the intermolecular forces of attraction within the liquid or the solid. The lower the vapor pressure, the stronger the forces of attraction between the particles. Figure 3: Vapor pressure curves for various liquids. The vapor pressure of a material depends on temperature, and it increases as the temperature rises. Fig. 3 shows the vapor pressure curves for various liquids in comparison with one another. Figure 4: Vapor pressure curve for a material in its solid and in its liquid phases (1-material system). Figure 5: State or phase diagram of a 1material system. BÜCHI Labortechnik AG Version A
10 Melting Point Laboratory guide Fig. 4 shows the vapor pressures for the solid and the liquid phases of a material. At the pressure where the vapor pressures for these two phases are the same, the equilibrium for melting (or freezing) is present. Expanding this diagram to include the other transitions between the three physical states produces what is referred to as a state or a phase diagram. The phase diagram for a material is a pressure-temperature diagram showing under what conditions a material is a solid, a liquid, or a gas. The zones are divided from one another by phase boundaries that represent pairs of values (p,T) at which the two phases are in equilibrium with one another (melting point, vapor pressure, and sublimation curves). For given pressure-temperature conditions, one can determine from a phase diagram the phase or phases in which the given material may exist (cf. Fig. 5). At the so-called «triple point» – that is, at that point where the three curves meet – the three physical states (solid/liquid/gaseous) can coexist. The location of the triple point cannot be altered. There is only one characteristic pair of values (pressure/temperature) for any given material. The best known triple point is that for water, which lies at 273.16 K (0.01 C). The vapor pressure curve ends at the critical point. Above this critical temperature, a material can no longer exist as a liquid. There is therefore no longer a limit surface between the liquid phase and the gaseous phase. The conditions at this transition point (pressure/temperature) can be obtained from reference tables. 2.3 What happens during melting? In order to melt a solid, you must break its lattice structure by supplying energy to counteract the forces of attraction holding the particles together. The greater the effective forces between the particles, the more energy you need to destroy the lattice structure. The particles in a crystalline lattice do not exactly stand still, but vibrate slightly about their spatially fixed position (thermal movement). For each particle, the mean kinetic energy is or, in other terms, m: mass of the particle v: velocity k: Boltzmann constant ( 1.3806 · 10 –23 J/K) T: temperature The higher the temperature, the more energetic the particles become and the more strongly they vibrate. As a result of their stronger movement, the particles require more space as the amount of warming increases – the material expands. Finally, at the melting point, the vibrations of the particles are strong enough so that the lattice forces can no longer maintain the orderly arrangement – the solid material melts. The melting point of a material is defined as that temperature at which, under normal atmospheric pressure (101.3 kPa), the solid/liquid equilibrium sets in. At the melting point, then, the solid substance is in a state of equilibrium with its molten state. Or, in other terms: at the melting point, the liquid and the solid both have the same vapor pressure (cf. Fig. 1). The molecules of a substance do not have to be separated completely from one another during melting (as during boiling), and the resultant change in volume is relatively slight. This means scarcely any volume works in opposition to the atmospheric pressure that needs to be exerted. Because a small change in pressure has only a slight effect on the melting point of a substance, external pressure may be neglected when determining the melting point. The heat supplied to a material BÜCHI Labortechnik AG Version A
during the melting process does not cause any change in temperature because the total amount of (heat) energy supplied is needed to overcome the forces of attraction between the particles (cf. Fig. 2). The energy used to accomplish this is referred to as the melting heat or the melting enthalpy ΔHmelt. E.g., for water: H2O (s) H2O (l) ΔH 6.01 kJ mol-1 The same amount of energy that was needed to melt a material is released when freezing it. That means that the enthalpy change when the phase transition runs in the opposite direction has the opposite mathematical sign: H2O (l) H2O (s) ΔH – 6.01 kJ mol-1 Substance Formula Melting point ( C) Molar melting heat (kJ/mol) ΔH f Water H2O 0 6.01 Hydrogen sulfide H2S - 85.5 2.38 Ammonia NH3 - 77.9 5.96 Methane CH4 - 182.7 0.95 Table 2: Melting point and molar melting heat for several important substances. 2.4 The boiling point – what happens during evaporation? The boiling point is defined as that pair of values for pressure and temperature identifying the condition of a chemically homogeneous substance at which the substance passes from a liquid state to a gaseous state by boiling. The boiling point is reached when the vapor pressure of a liquid becomes equal to the external pressure. The forces of attraction between the particles are then no longer strong enough to hold the particles together – the liquid boils. The process of evaporation does not start suddenly at the boiling temperature. Even at lower temperatures, there is already a state of equilibrium present between the liquid and the gaseous phases. At the boiling point, however, the vapor pressure becomes so great that the atmosphere is pushed back and evaporation can take place freely. The boiling temperature of liquids is determined by the external pressure upon the liquid and the forces of cohesion between the liquid particles. The vapor pressure curve (cf. Fig. 3 and Fig. 4) shows the boiling points of a liquid under various different external pressures. Liquids with a very high normal boiling point can be brought to boil at a lower temperature by reducing the pressure upon them. BÜCHI Labortechnik AG Version A
12 Melting Point Laboratory guide The melting point, the boiling point is strongly pressure-dependent. The Clausius-Clapeyron equation describes the relationship between the vapor pressure and the temperature of a liquid: T1 and T2: two different temperatures of the liquid p1 and p2: vapor pressures of the liquid at the temperatures T1 and T2 ΔHv: molar evaporation heat of the liquid ( the amount of heat required to evaporate 1 mol of the liquid) R: ideal gas constant 8.314 J · mol –1 · K–1 log The Clausius-Clapeyron equation can also be written in a general form as a straight line equation in which «p» again stands for the vapor pressure of the liquid and «T» its temperature: This equation is now in the form of the general equation for a straight line, y a x b. Thus, graphing the logarithm of the vapor pressure against the reciprocal values for temperature produces a straight line on which the vapor pressure of the liquid at various temperatures can be read. The evaporation heat of the liquid can be calculated from the slope of the straight line. Because the boiling points of liquids as shown in the tables are always those for a standard pressure of 1013 bar (mean atmospheric pressure at sea level), these values – the so-called «normal» values – can be used as direct indicators of the cohesive forces within the liquid (cf. Tab. 3). Substance Formula Boiling point in C (1013 bar) Molar evaporation enthalpy ΔHv in kJ · mol-1 Water H2O 100.0 40.7 Benzene C6 H 6 80.1 30.8 Ethanol C2H5OH 78.5 36.8 Chloroform CHCl3 61.3 29.4 Table 3: Normal boiling points and molar evaporation enthalpy of several substances When the increase in heat is constant, the temperature of the liquid increases evenly prior to boiling. Then, at the boiling point, the temperature remains constant until all of the liquid has been evaporated: the energy supplied during the boiling process is being utilized (cf. Fig. 2). The greater the amount of heat supplied, the faster the liquid goes into the gaseous phase, but its temperature does not rise while this is happening. BÜCHI Labortechnik AG Version A
Melting Point Laboratory guide 13 While pure materials (elements and compounds) have a constant boiling pressure at any given pressure, mixtures of several materials (e.g., solutions of solids, gasolines) behave differently when boiling: They have a so-called boiling range, i.e., their boiling pattern extends between defined boiling limits. Dissolving a solid in a liquid always reduces the vapor pressure of the liquid. More energy is then needed before the vapor pressure of the liquid equals the external pressure. This raises the boiling temperature of the liquid (cf. Fig. 2). Raoult’s Law describes this relationship. The relative lowering of vapor pressure here depends only on the number Ns of particles dissolved. The nature of the dissolved material makes no difference. Raoults’s Law p/p: relative lowering of vapor pressure Ns: number of particles dissolved N1: number of particles of the solvent 2.5 The range between the boiling and the melting point Pure materials (molecular compounds, salts) have «sharp», i.e. precisely defined, melting points: The change in temperature between the solid and the liquid takes place within a very small temperature range of 0.5 to 1 C. Below the melting point, the material remains solid; above it, it is in liquid form. The melting temperature of a crystalline material depends on its lattice stability. The greater the forces of attraction between the particles in the lattice structure, the higher the melting temperature. Amorphous solids do not have one single defined melting temperature, but melt over a broad range of temperatures within which the amorphous body gradually softens and liquefies. The phase transition from solid to liquid for contaminated solids likewise takes place over a range of temperatures that may be as much as several degrees. As a rule, a broad range of melting temperatures indicates contamination of the substance. But it may also be an indication that the substance is decomposing during the melting process. Thus, the way in which a material melts provides some first indications of its purity, and the location of the melting point is used for purposes of identifying it. BÜCHI Labortechnik AG Version A
14 Melting Point Laboratory guide 2.6 Melting point depression and the mixed melting point 2.6.1 Melting point depression Even minimal amounts of impurities cause a change in the melting behavior of a pure substance (melting point depression) and usually result in a considerable broadening of its melting range as well. The theory of melting point depression can be explained based on the vapor pressure phenomenon: The displacement of the vapor pressure curve due to the contamination of a substance lowers its melting point. A soluble contaminant therefore weakens the lattice forces within a solid. The graph in Fig. 6 shows this relationship. Figure 6: Lowering of the melting point and raising of the boiling point. Contaminants weaken the lattice forces within a solid, bringing with it a depression of the melting point. The vapor pressure in a liquid is reduced whenever a substance is dissolved in it. As a result, its boiling temperature rises. 2.6.2 Mixed melting point The phenomenon of melting point depression can be used for the determination of unknown pure substances. For example, when you measure the melting point of an unknown substance A at a temperature 180 C, you will find from the reference tables that this is the right melting point for 10 different substances. Substance A can be identified by determining its mixed melting point: A is mixed one-by-one with small amounts of the other substances, and the mixed melting point is determined in each case. Whenever the melting point of A is reduced by mixing a small amount of another substance B with it, the two substances cannot be identical. If, however, the melting point of A does not change, the substance B that was added was identical to A: A has been identified. BÜCHI Labortechnik AG Version A
Melting Point Laboratory guide 15 2.6.3 The eutectic point Two or more materials that form a homogenous molten product with one another (but are not miscible in their solid state, because one is dealing in each case with pure components) behave eutectically when mixed in certain proportions with one another. This means that there is a certain mixing ratio for these materials at which they act like a pure material when melting, i.e., the mixture has a sharply defined melting point. Figure 7: Mixing diagram for a eutectic product. The melting points for the pure components A and B are shown on the ordinates. These are joined by the melting diagram of the mixtures. The melting curve drops off from Ta and Tb to the melting point of the eutectic product, the eutectic point. When the mixing ratio of the substances differs from the eutectic mixture, the mixture melts at the beginning in eutectic proportions. The remaining molten eutectic and the crystals of the two pure substances in it melt over a range of melting temperatures BÜCHI Labortechnik AG Version A
16 Melting Point Laboratory guide 3 Principles and methods of melting point determination 3.1 Methods of melting point determination The procedural rules for melting point determination are defined in the pharmacopoeias (Medical Handbooks/cf. Chap. 5.1). These agree in describing the capillary method as the basic method for melting point determination. The medical handbooks even explain minimum requirements for the design of the apparatus and for carrying out the determination. In addition to the capillary method, the pharmacopoeias also describe other possible methods that may be called upon in special cases for melting point determination. 3.1.1 Determining the melting point in the capillary tube Melting temperature determined using the capillary method is that temperature at which the last solid particle from a compact column of the substance in the melting point tube goes over into the liquid phase. The determination thus uses the so-called «clear» melting point since this represents an unmistakable criterion for recording the melting point. Figure 8: Melting point determination in the glass beaker and in the Thiele apparatus. BÜCHI Labortechnik AG Version A
Melting Point Laboratory guide 17 The standard capillary method described in the pharmacopoeias starts with a heated liquid bath equipped with a thermometer for measuring the temperature. A glass capillary tube containing the substance to be determined is introduced into this liquid in such a way that the substance in the capillary tube is located close to the mercury reservoir on the thermometer. At the clear melting point, the temperature reading on thermometer is taken. The capillary method described in the pharmacopoeias starts from visual detection of the melting point. More modern instruments for melting point determination enable detection of the melting point not only in the traditional way, visually, but also automatically (cf. Chapter 4.1.1). In addition to the capillary method, the medical handbooks also provide another method that can be called upon «in certain exceptional cases» for determining the melting point – the so-called «open capillary method» (rising tube melting point). This method is of importance mainly for the investigation of solid greases (e.g., mixtures of various glycerides) because what is observed here on heating is not really a melting point in the strictest sense of the word, but rather a gradual softening and liquefying of the substance. Fig. 8 shows two possible instruments that operate using the «bath method» described in the pharmacopoeias. 3.1.2 Immediate melting point Some materials decompose during the melting process or show a tendency toward polymorphous modifications. The capillary method is not suitable for use with such substances, which is why the pharmacopoeia provides for using the flash melting point in such cases. In this method, the temperature does not affect the substance at all prior to its reaching its melting point. This method uses a heatable metal block (e.g., of brass) that is heated up evenly. A few crystals of the substance to be determined are scattered on this block at regular intervals. The first temperature at which the substance melts immediately on contact with the metal block is read off as T1. The heating of the block is discontinued, and while it is cooling down, small samples of the substance are again scattered on the block at regular intervals. T2 is the temperature at which the substance stops melting immediately on contact with the metal. The immediate melting point is then obtained from the formula: Mainly, there are two variants of such a metal block that have worked out well in practice: the rectangular Bloc Maquenne that is used predominantly in France, and the metal block of the DAB7 that is commonly used in Germany. The Kofler heating stand is particularly well-suited for series measurement of the immediate flash point where no special requirements are made with regard to accuracy of measurement. Fig. 9 shows the various instruments available. BÜCHI Labortechnik AG Version A
18 Melting Point Laboratory
3.1.1 Determining the melting point in the capillary tube 16 3.1.2 Immediate melting point 16 3.2 Principles of melting point determination 18 3.2.1 Melting point determination according to the pharmacopoeia 19 3.2.2 Thermodynamic determination of melting points 20 3.3 Melting point determination yesterday and today - an overview 21
Chapter 2: Chemical Bonding below: (i) The type of bonding in X will be A. ionic B. electrovalent C. covalent D. molecular (ii) X is likely to have a A. low melting point and high boiling point B. high melting point and low boiling point C. low melting point and low boiling point D.
WITEPSOL E 85 melting point 42–44 C HV 5–15 WITEPSOL S 51 melting point 30–32 C HV 55–70 WITEPSOL S 55 melting point 33.5–35.5 C HV 50–65 WITEPSOL S 58 melting point 31.5–33.5 C HV 60–70 WITEPSOL W 32 melting point 32–33.5 C HV 40-50 WITEPSOL W 25 melting point 33.5–35.5 C HV 20-30
Melting Point Determination Melting Point Determination Trustworthy, Automatic, Exact. 3 95 100 105 110 115 120 125 of light through the sample and hence the light intensity measured by a 130 135 100 80 60 40 20 0 The melting point and its detection The melting point is a characteristic property of a substance. .
melting point of the pure solids. The melting point helps to identify unknown samples. we can distinguish between the three sugarsknoen as glucose (MP 150 C), fructose (MP 103-105 C), and sucrose (MP 185-186 C) for example, by determining the melting point of a small sample. The melting point helps to characterize new compounds.
SMP40 Automatic melting point apparatus, complete with pack of 100 melting point tubes, closed at both ends. SMP30/1 Accessory printer with power supply, only for use with SMP30 SMP2/1 Glass melting point tubes, closed at both ends, pack of 100 SMP1/4 Glass melting point tubes, open at both ends, pack of 100
Melting point :( mp) 1- Close one end of a standard melting -point tube in a Benzene flame. 2-Inroduce the sample to a depth of about 2mm at the sealed end of the tube. 3-place the tube in an electrically heated melting-point apparatus. 4- Adjust the rate of heating so that the temperature rises about 3-4 for a min.
For more information regarding melting point, refer to the corresponding literature: The Laboratory Assistant 94187 Melting Point M-560, Operating Manual numbers 93251-93255 Melting Point M-565, Operating Manual numbers 93256-93260 1.2 Abbreviations Chemicals: PTFE Polytetrafluoroethylene PP Polypropylene PE Polyethylene
another language. A “Secondary Section” is a named appendix or a front-matter section of the Docu-ment that deals exclusively with the relationship of the publishers or authors of the Document to the Document’s overall subject (or to related matters) and contains noth-ing that could fall directly within that overall subject. (For example .
